A glow plug is used as an assisting heat source in compression ignition type internal combustion engines, such as Diesel engines. The glow plug includes: for example, a heater unit configured to heat a combustion chamber in an internal combustion engine; a pressure sensor configured to measure the pressure in the combustion chamber; and a coupling member in a thin film shape joined with the heater unit and with a housing and configured to hold the heater unit in a deformable manner in an axis line direction of the glow plug. In this glow plug, the coupling member and the heater unit, and the coupling member and the housing are joined together by punching laser welding.
In the case of joining respective members together by punching welding, the interval between the members that is about 1/10 of the thickness of a member to be welded can generally maintain the bonding strength of a welded part. In other words, in the process of welding the heater unit with the coupling member of the glow plug, the bonding strength of the welded part can be maintained when the interval between the respective members is about 1/10 of the thickness of the coupling member that is the member to be welded.